If you mean you have two separate use years and thus two membership numbers, then the 24 rule should apply to each one separately, although I have not seen reports of that one being tested by a member. Also, if you are going to try that, you better not transfer points from one use year to the other before doing so because that would put all the points in one membership for the purpose of purchasing one time use points.
If you mean you bought a contract with a use year and then you bought another one with the same use year, which results in both being under the same membership number, then you will be limited to 24.